The Zookeeper first appeared in an early version of SLASH'EM (NetHack-- 3.0.10) but was dropped from the code at the time the quest branch was ported into that variant. The role was later revived and given a quest in Slash'EM Extended.

Gods

The Zookeeper's pantheon comes from Norse mythology:

Lawful: Balder

Neutral: Edda

Chaotic: Hagen

History

The Zookeeper's first appearance was in SLASH'EM precursor NetHack-- 3.0.10, as one of nine new roles in addition to the twelve in the contemporary version of NetHack. The discussion thread in which the authors first announced the variant suggests that some of the new roles were taken from a list proposing a role for every letter of the alphabet. See here for the relevant post.

After the release of NetHack 3.1.3 in 1993, NetHack-- was updated to NetHack-- 3.1.3 by porting some of the changes from NetHack-- 3.0.10 into a patch for the newest version. Due to some changes in the vanilla code, however, some content was removed to improve compatibility with NetHack. Most significantly, NetHack 3.1 had seen the addition of the Quest branch. To avoid the challenge of fitting full-length quests for the roles that had been added in NetHack-- 3.0.10 into the patch code, those roles were simply left out of the patch.

There is some evidence that the developer(s) of SLASH may have wanted to bring back some of the roles, including the Zookeeper, as the DAT folder for SLASH 6 contains unused maps for quest levels for this and other roles that are not actually present in the version. The nemesis would have been a Y named "The Great Black Ape", and the quest artifact would have been a magic whistle called The Golden Whistle. (Lord Carnarvon appears as the quest leader, probably a holdover from the Archeologist quest.) The code for the maps indicates that the quest would feature numerous felines and apelike creatures.

The Zookeeper role, along with the other eight new roles in NetHack-- 3.0.10, made its reappearance in the variant Slash'EM Extended. It was also carried over, with some tweaks, into SLASHTHEM, a variant of Slash'EM Extended v75.